PCI: expose function reset capability in sysfs

Some devices allow an individual function to be reset without affecting
other functions in the same device: that's what pci_reset_function does.
For devices that have this support, expose reset attribite in sysfs.

This is useful e.g. for virtualization, where a qemu userspace
process wants to reset the device when the guest is reset,
to emulate machine reboot as closely as possible.

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Documentation/ABI/testing/sysfs-bus-pci

@@ -84,6 +84,16 @@ Description:
 		from this part of the device tree.
 		Depends on CONFIG_HOTPLUG.
 
+What:		/sys/bus/pci/devices/.../reset
+Date:		July 2009
+Contact:	Michael S. Tsirkin <mst@redhat.com>
+Description:
+		Some devices allow an individual function to be reset
+		without affecting other functions in the same device.
+		For devices that have this support, a file named reset
+		will be present in sysfs.  Writing 1 to this file
+		will perform reset.
+
 What:		/sys/bus/pci/devices/.../vpd
 Date:		February 2008
 Contact:	Ben Hutchings <bhutchings@solarflare.com>

drivers/pci/pci-sysfs.c

@@ -916,6 +916,24 @@ int __attribute__ ((weak)) pcibios_add_platform_entries(struct pci_dev *dev)
 	return 0;
 }
 
+static ssize_t reset_store(struct device *dev,
+			   struct device_attribute *attr, const char *buf,
+			   size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	unsigned long val;
+	ssize_t result = strict_strtoul(buf, 0, &val);
+
+	if (result < 0)
+		return result;
+
+	if (val != 1)
+		return -EINVAL;
+	return pci_reset_function(pdev);
+}
+
+static struct device_attribute reset_attr = __ATTR(reset, 0200, NULL, reset_store);
+
 static int pci_create_capabilities_sysfs(struct pci_dev *dev)
 {
 	int retval;
@@ -943,7 +961,22 @@ static int pci_create_capabilities_sysfs(struct pci_dev *dev)
 	/* Active State Power Management */
 	pcie_aspm_create_sysfs_dev_files(dev);
 
+	if (!pci_probe_reset_function(dev)) {
+		retval = device_create_file(&dev->dev, &reset_attr);
+		if (retval)
+			goto error;
+		dev->reset_fn = 1;
+	}
 	return 0;
+
+error:
+	pcie_aspm_remove_sysfs_dev_files(dev);
+	if (dev->vpd && dev->vpd->attr) {
+		sysfs_remove_bin_file(&dev->dev.kobj, dev->vpd->attr);
+		kfree(dev->vpd->attr);
+	}
+
+	return retval;
 }
 
 int __must_check pci_create_sysfs_dev_files (struct pci_dev *pdev)
@@ -1037,6 +1070,10 @@ static void pci_remove_capabilities_sysfs(struct pci_dev *dev)
 	}
 
 	pcie_aspm_remove_sysfs_dev_files(dev);
+	if (dev->reset_fn) {
+		device_remove_file(&dev->dev, &reset_attr);
+		dev->reset_fn = 0;
+	}
 }
 
 /**

drivers/pci/pci.c

@@ -2261,6 +2261,22 @@ int __pci_reset_function(struct pci_dev *dev)
 }
 EXPORT_SYMBOL_GPL(__pci_reset_function);
 
+/**
+ * pci_probe_reset_function - check whether the device can be safely reset
+ * @dev: PCI device to reset
+ *
+ * Some devices allow an individual function to be reset without affecting
+ * other functions in the same device.  The PCI device must be responsive
+ * to PCI config space in order to use this function.
+ *
+ * Returns 0 if the device function can be reset or negative if the
+ * device doesn't support resetting a single function.
+ */
+int pci_probe_reset_function(struct pci_dev *dev)
+{
+	return pci_dev_reset(dev, 1);
+}
+
 /**
  * pci_reset_function - quiesce and reset a PCI device function
  * @dev: PCI device to reset

drivers/pci/pci.h

@@ -16,6 +16,7 @@ extern void pci_cleanup_rom(struct pci_dev *dev);
 extern int pci_mmap_fits(struct pci_dev *pdev, int resno,
 			 struct vm_area_struct *vma);
 #endif
+int pci_probe_reset_function(struct pci_dev *dev);
 
 /**
  * struct pci_platform_pm_ops - Firmware PM callbacks

include/linux/pci.h

@@ -276,6 +276,7 @@ struct pci_dev {
 	unsigned int	state_saved:1;
 	unsigned int	is_physfn:1;
 	unsigned int	is_virtfn:1;
+	unsigned int	reset_fn:1;
 	pci_dev_flags_t dev_flags;
 	atomic_t	enable_cnt;	/* pci_enable_device has been called */